This project studies the structure and function of a cell organelle, the cilium, that is crucial to normal respiratory function in man. Model systems are examined; a major tool is electron microscopy. An important facet has been the development of the sliding microtubule model of ciliary motility, two aspects of which are currently under investigation: 1. the mechanism of bend formation in the axoneme; 2. the mechanism of ciliary arrest. Previously, we (Warner and Satir, 1974, J. Cell Biol. 63 35) have demonstrated that the radial spokes attached to each ciliary doublet microtubule can be used to measure sliding between pairs of doublets. Currently, procedures have been derived for a rapid analysis of spoke organization and therefore sliding in three-dimensions. Critically-point dried intact and splayed ciliary axonemes are examined. Spoke displacement gives rise to several patterns, including 3 start single and double helices in the intact cilia and similar lattice arrangements in the unrolled cilia, which we conclude represent variable amounts of co-ordinated sliding that have occurred basal to the regions examined. The amount of sliding per spoke period is a constant for any one cilium, supporting a quantal bending model where spokes become attached at the point of bend growth. We are presently examining the question of whether Ca ions turn the sliding system of ciliary microtubules on and off. The calcium specific ionophore A23187 offers an experimental tool for controlling Ca ions entry into the cell cytoplasm. Initial results indicate that in the presence of Ca ions and ionophore, cilia are arrested.